This invention relates to an improvement of a universal joint (swivel) for fishing ropes.
Usually, lines are used to set a fishing net in a predetermined fishing zone and to recover it by a trawler. The lines are affected greatly by movement of the fishing net, the wave action, and so forth. These actions twist the lines severely, decreasing their durability.
Generally in order to avoid these problems, a universal joint, called a swivel, is inserted into a connection point between two adjacent lines to allow free motion of the line.
A conventional swivel comprises a U-shaped fork and a ring of a closed-loop form coupled to each other at the base of the fork. The fork and the ring can make relative rotation about the spindle of the swivel located along the direction in which the lines are pulled. Such fork has two arms adapted to retain a pin which is screwed into holes formed in their ends. The pin so fitted in bridges in both arms of the fork.
A C-shaped hook or a shackle is mounted on an end of one of two lines to be connected together. A loop for having such pin passed therethrough is formed in an end of the other line, the loop being produced by bending the end portion.
The C-shaped shackle is connected to the ring of the swivel, while the loop is connected to the fork of the swivel, via the pin.
When the two lines thus connected together by the swivel begin to twist relative to each other, the ring and fork of the swivel rotate relative to one another and absorb the twist, thus avoiding damage to the lines due to the twist.
The two connected adjacent lines are, however, affected by bends as well as twists. Since the swivel is unable to absorb the bends, the bent lines undergo rubbing or deformation at the junction between the line and the ring or fork. Thus, the line under bending action tends to be damaged.
Particularly, the loop of the line can be easily damaged because it is rubbed at a sharp-angled portion formed by the intersection of the pin and the fork arm. Also, rubbing occurring between the pin and the loop may loosen the pin screwed into the holes of the arms, thereby causing it to slip off the fork.